Blind rivet and method of assembly

ABSTRACT

A blind rivet and a method of assembly comprising a tubular shell and mandrel in combination. The mandrel comprises a stem and a radially-enlarged head which in use forms a blind head to the shell to set the rivet, in which either the head of the mandrel or the bore of the shell is formed with a plurality of depressions the bases of which lie on a notional circle having a diameter which, where the depressions are formed in the head of the mandrel, is less than the bore of the shell or, where the depressions are formed in the bore of the shell, is greater than the diameter of the head of the mandrel. The depressions, which are preferably generally longitudinally disposed, define ribs, ridges or other protrusions therebetween which in use and on pulling the mandrel into the shell bore extend radially beyond the bore of the shell, so that material of the shell becomes displaced by contact with the ridges and occupies the depressions. The invention may be applied either to pull-through, or self-plugging rivets.

This invention relates to a blind rivet. A blind rivet is one that. canbe inserted and set by access to one side only of apertured members tobe riveted together.

Blind rivets are either of the pull-though type or of the self-pluggingtype. In both types, the rivet comprises a tubular shell having apreformed radial head at one end; the shell is threaded on a mandrelwhich has a head adjacent to the tail end of the shell. In use, theshell is inserted, tail end first, through the apertures in the membersto be riveted until the shell head contacts the nearer member and theshell tail protrudes beyond the further member. In order to set therivet, the shell is supported by an abutment and the mandrel is thenpulled through the shell bore so as to form a blind head which togetherwith the preformed head clamps the members together and also expands theshank of the rivet. With pull-though rivets, the mandrel is pulledcompletely through the bore and can be re-used with another shell,whereas with self-plugging rivets the stem of the mandrel is providedwith a narrowed neck portion known as a breakneck which defines theposition where the mandrel breaks under tension applied by the settingtool when the blind head is formed, leaving the head and remote part ofthe stem in place in the set rivet.

Rivets of the pull-though type are well known and a particular design isdescribed in UK patent 1323873 whereas the rivets of the self-pluggingtype are described in UK patent number 2330639.

Hitherto, the performance of pull through rivets has been markedlyinferior to that of self-plugging or break stem rivets. It is thepurpose of the present invention to provide a riveting system whichshows distinct advantages over existing systems in complexity, cost, andperformance. In addition the safety especially of pull throughrepetition riveting systems in which rivet shells are threaded on a longmandrel is a serious problem since if the mandrel breaks under thesetting loads it may be projected from the partially placed rivet athigh speed. It is a further object of the present invention to provide amethod of placing rivets, especially repetition rivets, in whichprojection of a part of the mandrel in the case of mandrel breakage isinhibited. It is also, however, an object to provide ahigher-performance self-plugging rivet.

In one aspect, the present invention provides a blind rivet comprising atubular shell and mandrel in combination, the mandrel comprising a stemand a radially-enlarged head which in use forms a blind head to theshell to set the rivet, in which either the head of the mandrel or thebore of the shell is formed with a plurality of depressions the bases ofwhich lie on a notional circle having a diameter which, where thedepressions are formed in the head of the mandrel, is less than the boreof the shell or, where the depressions are formed in the bore of theshell, is greater than the diameter of the head of the mandrel.

Preferably, the depressions are formed in the head of the mandrel andthe bore of the shell is a plain cylinder. The depressions, which arepreferably generally longitudinally disposed, that is, have a majorcomponent parallel with the axis of the rivet, define ribs, ridges orother protrusions therebetween which in use and on pulling the mandrelinto the shell bore extend radially beyond the bore of the shell, sothat material of the shell can be displaced by contact with the ridgesand occupies the depressions. The material of the mandrel, or at leastthe head thereof, is preferably harder than the material of the shell.

To permit the head of the mandrel to enter the bore of the shell, theleading edge of the ridges may be provided with a chamfer to form anannular angled segmented shoulder between the stem and head of themandrel.

For pull-through rivets according to the present invention, the stem ofthe mandrel is a plain cylinder whereas for self-plugging rivets thestem of the mandrel is provided with a breakneck adjacent theradially-enlarged head.

In use, when the mandrel head is drawn through the shell bore, the headinitially expands the tail of the shell to form a blind head whichclamps the apertured members together with out substantially distortingthe bore of the shell. However, when the head of the mandrel begins toenter that part of the shell bore which is within the apertured membersbeing fastened, the ribs, ridges or other protrusions defined by thedepressions in the mandrel head displace material from the rivet shellinto the depressions as well as expanding the shell radially, therebyensuring that the shell shank effectively fills the hole in theapertured members. It is necessary that the depressions have sufficientvolume to accommodate the material displaced from the shell by theridges and. this determines the diameter of the circle through the baseof the depressions.

Since as the mandrel is drawn into the rivet bore the depressions in thestem become filled with shell material, the mandrel is positivelyprevented from being pushed out and thus if the mandrel breaks duringthe setting process a dangerous incident is prevented.

In a conventional pull through riveting system, the diameter of the boreof a set rivet is equal to the diameter of the head of the mandrel. Inthe present invention and although the major diameter of the bore of theset rivet is determined by the major diameter of the mandrel head, thedepressions in the mandrel head result in radial protections into thebore which substantially increase the strength of the set rivet. Afurther aspect of the invention is that of providing a set rivet whichcarries projections in the rivet bore.

In a conventional self-plugging riveting system, the head and remotestem end of the mandrel remain in place in the set rivet and, except forsome slight embedding, the head of the mandrel does not enter the shellbore of the fully-set rivet. In the present invention, the head of themandrel initially enters the shell bore in the tail end region thereofto form the blind head and thereafter enters that part of the borewithin the apertured members to be fastened together, in the same way aswith the pull through rivet. However, in this case the bore of the noseof the placing tool is a close fit on the mandrel so that, when the headof the mandrel contacts the nose of the placing tool, the tension in thestem of the mandrel is increased and the stem breaks at the breakneck,thus resulting in the bore of the rivet shank being filled with the headof the mandrel retained therein. The displacement of shell material intothe depressions in the head of the mandrel results in the shell andmandrel head being locked together and a stronger set rivet once thestem has fractured.

In blind rivets according to the invention, the depressions arepreferably in the form of grooves or channels and are preferablyoriented substantially parallel with the longitudinal axis of themandrel. However, the grooves or channels may be skewed in afrusto-helical disposition whereby on application of setting forcesthere is a tendency for the mandrel to twist about its longitudinal axisas the head thereof engages the bore of the shell. This may be ofparticular advantage with a rivet of the self-plugging type where stemfracture would occur on a combination of tension and shear forcesapplied as between the near or proximal end of the stem and the remoteor distal end adjacent the head.

Embodiments of the invention will now be described by way of example andwith reference to the accompanying drawings in which:-

FIG. 1 is a longitudinal section through the shell of a pull-throughrivet;

FIG. 2 is a side elevation of a mandrel for use with the shell of FIG.1;

FIG. 3 is a section of the line A-A′ of FIG. 2;

FIG. 4 shows the rivet assembled on a mandrel and inserted in sheets tobe riveted together;

FIG. 5 shows the initial stage of setting the rivet;

FIG. 6 shows the blind head fully formed;

FIG. 7 shows the mandrel partially drawn through the rivet bore;

FIG. 8 is a section through the shank of the rivet of FIG. 7;

FIG. 9 shows the rivet fully set;

FIG. 10 is a section through the shank of the set rivet;

FIG. 11 is a longitudinal section through the shell suitable for aself-plugging rivet;

FIG. 12 is a side elevation of a mandrel for a self-plugging rivet; and

FIG. 13 is a section through a self-plugging rivet which has been set.

Referring first to FIG. 1, the shell 17 comprises a tubular body 11having a concentric bore 12 and at one end a radially enlarged head 13which carries a recess 15. The tail end 16 of the shell is flat and atright angles to the shell axis.

The mandrel shown in FIG. 2 is elongate and generally cylindrical. Atone end it has a radially enlarged head 22 which is an integral part ofthe mandrel and is joined to the shank of the mandrel 21 by taperedportion 23. The shank has an end part 32 remote from the head forgripping by a placing tool, as described later. The shank of the mandrelis preferably sufficiently long so that a plurality of rivet shells canbe threaded on it and fitted to a rivet placing tool which is arrangedto feed rivet shells sequentially to the head end of the mandrel as theprevious rivet shell is placed in the sheets to be riveted together.This type of tool is well known and will not be described further. Thehead of the mandrel carries recesses 24 the diameter of the root circleof which is less than the diameter of shank 21 and the outer surface ofthe head comprises ribs 33. Recesses 24 terminate at their end adjacentto the mandrel shank in an internal taper 26 which is complementary tothe external taper so that the overall cross section of the mandrel issubstantially constant. In the Figures, four ribs and correspondingrecesses are shown. In practice this is probably the minimum number ofribs which can be used but a greater number of ribs may be used forlarger diameter rivets. The shank of the mandrel 21 is a close fit inthe bore 12 of the rivet 17.

FIG. 3 shows a cross section of the mandrel head.

FIG. 4 shows the rivet shell 17 threaded on the mandrel shank 21 andinserted in the holes 27 and 28 in sheets 29 and 30 respectively. Therivet head is supported on the nose of a suitable placing tool 31 whichis arranged to pull the stem part 32 relative to the rivet body to setthe rivet.

In FIG. 5 the mandrel 32 has been pulled into the tail of the rivetexpanding it and forning a blind head 35 and beginning to draw sheets 29and 20 together and closing the gap 34 between the sheets.

FIG. 6 shows the blind head fully formed and sheets 29 and 30 pulledtogether closing gap 34.

In FIG. 7 the mandrel is entering the rivet bore between sheets 29 and30. The rivet shank has been expanded to fill the holes in the sheetsand the excess material displaced by ribs 33 is accommodated in recesses24 reducing the force required to set the rivet and minimising theelongation of the rivet shank which would tend to loosen the joint.

FIG. 8 is a cross section of the partially set rivet of FIG. 7.

FIG. 9 shows the rivet fully placed. In this type of rivet some shellmaterial may be dragged through the rivet bore and this material isaccommodated in the recess 15 of the rivet shell.

FIG. 10 is a cross section through the shank of the placed rivet of FIG.9 showing the projections 35 in the rivet bore which enhance the shearstrength of the rivet.

Referring to FIG. 11, a cross section of a rivet shell 42 suitable foruse in a self plugging rivet is shown. The shell consists of a shank 41and a head 46 and differs from the shell shown in FIG. 1 in that therecess 15 of FIG. 1 has been changed to the shape shown at 36 to conformto the shape of the nosepiece of a placing tool.

FIG. 12 shows the mandrel 43 for a self plugging rivet. This carries abreakneck 37 at the junction 40 of the pintail 38 and the head 39. Thecross section of the head is similar to the head of a pull through rivetmandrel as shown in FIG. 3 but the length of the head 39 issubstantially equal to the length of the shank of the rivet shell 41.FIG. 13 shows a placed self plugging rivet. The shell 42 has beenthreaded on the mandrel 43 and inserted through sheets 44 and 45. Thehead of the rivet 46 is supported by the nose 47 of a placing tool. Thebore 48 of the nose is a close fit on the pintail 38 of the rivet stem.A projection 49 on the front of the nose 47 is a close fit in the recess36 in the head of the rivet.

In operation, the pintail 38 is pulled by operation of the placing toolrelative to the nose 47. The formation of the tail of the rivet andexpansion of the shank between the sheets is identical to that of thepull through rivet previously described but when the placing sequence iscomplete the shoulders 50 of the mandrel head 39 adjacent to thebreakneck are arrested by the projection 49 on the nose of the placingtool 47 and the pintail breaks at the breakneck 40. Thus the rivet shellis fully plugged throughout its length and the mandrel break issubstantially flush with the head of the rivet.

It should be noted that this rivet has a grip range i.e. the range ofsheet thicknesses that can be joined together for which the upper limitis determined only by the length of the rivet shell. Obviously it is notdesirable that the rivet shell should be excessively long because of thedisadvantages of excessive weight and useage of raw material.

1. A blind rivet comprising a tubular shell and mandrel in combination,the mandrel comprising a stem and a radially-enlarged head which in useforms a blind head to the shell to set the rivet, in which the head ofthe mandrel is formed with a plurality of depressions the bases of whichlie on a notional circle having a diameter which is less then the boreof the shell and which define protrusions which extend radially beyondthe bore of the shell.
 2. A blind rivet according to claim 1, in whichthe depressions are generally longitudinally disposed and have a majorcomponent parallel with the axis of the rivet.
 3. A blind rivetaccording to claim 1 or 2, in which the material of the mandrel, or atleast the head thereof, is harder than the material of the shell.
 4. Ablind rivet according to claim 3, in which the leading edge of theprotrusions is provided with a chamfer to form an annular angledsegmented shoulder between the stem and head of the mandrel.
 5. A blindrivet according to claim 3, in which the depressions are in the form ofgrooves or channels which are disposed in a frusto-helical dispositionrelative to the axis of the mandrel.
 6. A blind rivet according to claim3, in which two or more shells are carried on a common mandrel.
 7. Ablind rivet according to claim 3, which has been set whereby the bore ofthe shell carries radial projections formed by passage therethrough ofthe head of the mandrel.
 8. (canceled)
 9. (canceled)
 10. A method ofsetting a blind rivet in apertured members, the method comprising thesteps of applying through the apertures a rivet tubular shell having apre-formed radial head so that the head is adjacent one of said memberand drawing though the shell a mandrel comprising a stem and aradially-enlarged head to form a blind head to the shell adjacent theother of said members, in which the head of the mandrel is formed with aplurality of depressions defining protrusions the bases of which lie ona notional circle having a diameter which is less than the bore of theshell and which extend radially beyond the bore of the shell, whereby,on drawing the mandrel through the shell, the protrusions displacematerial from the shell to occupy the depressions.